The invention relates to digital color transition improvement (DCTI), particularly to a DCTI method and system using fuzzy logic. (As understood herein, DCTI is also known as digital color transient improvement, which is a term used interchangeably with digital color transition improvement.)
Color video signals such as NTSC, PAL or SECAM types all have luminance (luma) component and chrominance (chroma) component. Specifically, the chroma signal bandwidth is usually narrower than luma signal bandwidth. As such, color edges changes occur much slower than luma edges changes. In other words, a chroma signal transition occurs fairly slower than a luma signal transition. Consequently, chroma signal edges/transitions usually appear degraded, thereby needing enhancement to xe2x80x9csharpenxe2x80x9d the chroma signal transitions.
Numerous prior art approaches exist for enhancing the slow transition color edges with edges that have steeper rising and falling times. One prior art approach generates an enhanced chroma signal transition by introducing to a chrominance signal an additional signal limited to a certain range. Yet another prior art approach generates an enhanced chroma signal transition by switching among a chrominance signal, and its delayed input signals. However, both prior art approaches in turn introduce additional problems.
Specifically, in the first prior art approach, adding a signal such as a difference signal of second order can lead to a fast chroma transition. Unfortunately, this fast chroma transition is generated with undesirable overshoot and undershoot that need to be xe2x80x9ccleaned awayxe2x80x9d by additional circuits. Also, introducing additional signals may increase noise to signal ratio. On the other hand, in the prior art second approach, an additional low pass filter is needed to smooth out input signal to avoid wrong switching choice. Also, a threshold level needs to be established before switching takes place. As such, this threshold level cannot be flexibly adjusted to a different threshold level that leads to a better enhanced chroma transition. Also, at certain threshold levels, the process of performing DCTI becomes sensitive and vulnerable to noise.
Thus, a need exists for performing DCTI without introducing signal overshooting or undershooting that need to be cleaned away with additional circuits. Also, a need exists for performing DCTI without increasing noise to signal ratio. A further need exists for performing DCTI without being restricted by threshold levels. Moreover, a need exists for performing DCTI without being sensitive to noise.
The invention provides digital color transition improvement (DCTI) without introducing signal overshooting or undershooting that need to be cleaned away with additional circuits. Also, the invention provides DCTI without increasing noise to signal ratio. The invention further provides DCTI without relying on any signal threshold level. Moreover, the invention provides DCTI without being sensitive to noise.
Preferably, a method is performed for digital color transition improvement (DCTI) on a N-pixel delayed signal of a digital chrominance signal. The method involves the digital chrominance signal, the N-pixel delayed signal and a 2N-pixel delayed signal of the digital chrominance signal. Using these three signals, a first and a second difference signals of first order are generated. Specifically, the first difference signal of first order is generated from the difference between the digital chrominance signal and the N-pixel delayed signal; the second difference signal of first order is generated from the difference between the N-pixel delayed signal and the 2N-pixel delayed signal. Furthermore, using the first and second difference signals of first order, a difference signal of second order is generated. In turn, the method and system generate a weighted sum of the digital chrominance signal and the 2N-pixel delayed signal. Specifically, the weighted sum is characterized by a weighing factor determined by applying a set of fuzzy inference rules to the first difference signal of first order and the difference signal of second order. The implementation of these fuzzy inference rules is performed by a fuzzy inference algorithm.
In addition, the method and system refine the weighted sum by generating a new (second) weighted sum of the N-pixel delayed signal and the weighted sum. Specifically, the new weighted sum is characterized by a new (second) weighing factor determined by applying a new (second) set of fuzzy inference rules to the first and second difference signal of the first order. In turn, the method and system generate a new weighted sum that has an enhanced digital color transition in comparison to the N-pixel delayed signal. Thus, the new weighted sum becomes the result of performing DCTI on the N-pixel delayed signal.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures.